The present invention relates generally to a roller conveyor system and more particularly to a motorized conveyor roller in which the motor and drive gear is contained inside the roller.
Typically, a roller conveyor system comprises a plurality of rollers rotatively mounted in a conveyor frame so as to define a path upon which articles are conveyed. Several rollers function as "drive rollers" to engage and propel the articles from one end of the conveyor path towards the opposite end. A conventional drive arrangement for such systems typically makes use of a separate electric motor, gear reducer, mounting frame, bearings, couplings and various hardware to provide a means of driving the rollers. The rollers themselves may be fitted with sprockets, or grooves to accommodate the drive chain or belt or, alternatively, the rollers may be driven a continuous flat belt which contacts the bottom airface of all the driven rollers. Such external drive arrangements take up a relatively large amount of space, require frequent servicing, and are not suited for dusty or wet environments.
To overcome these problems with external drive arrangements, motorized conveyor rollers have been used in the past in which the motor and drive gear is contained inside the roller. One such device is disclosed in the patent to Burger, U.S. Pat. No. 2,915,167, which is representative of the prior art in this field. Motorized conveyor rollers typically include a drum which is rotatably mounted on two end shafts, a motor fixedly secured to one shaft, and a gear reduction assembly which drives the drum.
There are several drawbacks associated with the motorized conveyor of the type shown in the patent to Burger. First, because the prior art motorized conveyor rollers use A/C motors, the roller must have a relatively large diameter in order to make room for the stator. Secondly, prior art designs make use a high voltage single phase or three phase alternating current which requires external wiring to deliver current to the motor. This external wiring is not only expensive and time consuming to install, but also poses a safety hazard to those working nearby.
Another concern with motorized conveyors is torque overload. When articles transported by the conveyor jam, it is desirable that the drive rollers stop rotating to protect not only the articles being transported, but also the motor and gear assembly. In some previous designs of motorized conveyor rollers, a clutch has been interposed between the motor and gear reducer assembly which slips at a predetermined torque. This arrangement, however, causes a relatively high degree of wear on the clutch parts since the motor rotates at substantially higher speed than the roller. This wear also causes the slip torque to vary unpredictably.
Yet another concern with motorized conveyors is with maintenance. Because the motor and gear assembly is located inside the roller tube, it is desirable to provide for easy access to internal components so that they can be serviced, replaced or repaired.